In conventional film/screen radiography, a body part of a patient is exposed to x-rays to produce a latent x-ray image in film. The exposed film is processed and ready for viewing by a radiologist or other medical made diagnostician. In many cases, it is desirable to have more than one copy of an x-ray image available for use by other medical personnel, for archiving, for transmission to a remote location, etc.
One method of making duplicate copies of radiographs has been by contact printing on direct-positive duplicating film. Because of the difficult set of requirements on the duplicating film, i.e., high maximum density (D max), gamma=-1, and wide dynamic range, it has been difficult to obtain accurate and inexpensive copies by this method. Other contact printing techniques, such as the thermal duplicating technique disclosed in U.S. Pat. No. 3,768,906, issued Oct. 30, 1973, inventors Michelson, et al; and U.S. Pat. No. 4,967,287, issued Oct. 30, 1990, inventor Nakatani, do not have high enough quality to be useful in radiographic film duplication.
In the case of other medical imaging modalities, such as computerized tomography (CT), or magnetic resonance imaging (MRI), the image is acquired, digitized, and stored on a magnetic or optical storage medium (disk, tape). Such an image may be printed, e.g., on a laser film printer and the film developed in a film processor. Multiple duplicates can be made by repeating the process. In doing so, however, one is limited by the relatively slow throughput time of the laser film printer/processor.
Laser thermal recording of images by means of analog ablation and/or evaporation techniques are known in the production of optical records and the like. (See, e.g., U.S. Pat. No. 4,000,492, issued Dec. 28, 1976, inventor Willens; U.S. Pat. No. 4,023,185, issued May 10, 1977, inventors Bloom et al.; and U.S. Pat. No. 4,097,895, issued Jun. 27, 1978, inventor Spong.) The ablated record can then be used to produce duplicates by optical contact printing (See U.S. Pat. No. 4,980,262, issued Dec. 25, 1990, inventors Thomas et al.), or by impression contact printing (See U.S. Pat. No. 4,285,056, issued Aug. 18, 1981).
The method of halftone printing as a means of rendering continuous tone imagery using ablation recording on thin metal (e.g., bismuth) layers is disclosed in U.S. Pat. No. 3,720,784, issued Mar. 13, 1973, inventors Maydan et at. (See also: Micromachining and Image Recording on Thin Films by Laser Beams, by D. Maydan, The Bell System Technical Journal, Vol. 50, No. 6, July-August 1971.) A projection copy of the record can be made by photographic or electrophotographic techniques.
None of the duplication techniques referred to in the last two paragraphs are advantageous in making duplicates of radiographic film because of high cost, slow duplicating speed, and impracticality.
Therefore, a problem exists in the need for a fast, convenient, and/or inexpensive technique for making duplicate copies of continuous tone black and white medical, radiographic, and other high quality images.